Lingual papillae

Hello everyone! It's Megan from Kenhub, and welcome to our tutorial on the lingual papillae. During this tutorial, we'll go over the anatomy and function of the different structures we can see in this image. So some of these structures include the filiform papillae, the vallate papillae, the fungiform papillae, the taste buds, the lingual tonsil and some associated glandular tissue. The only papillae we can't see in this image are the foliate papillae, however, they're located on the sides of the tongue and we're going to go through them later on in this tutorial.

So, to start with, let me give you a bit of an introduction on the lingual papillae. The lingual papillae are located on the dorsum or the upper surface of the tongue which we can see here. They are only located on the presulcal part of the tongue which is the part of the tongue anterior to the sulcus terminalis. The sulcus terminalis is this V-shaped groove highlighted in green and it separates the anterior two-thirds of the tongue from the posterior third. The dorsum of the tongue is covered by mucosa and the lingual papillae are essentially projections of this mucosa that gives the tongue its rough surface. So here we can see the sulcus terminalis with the vallate papillae sitting anterior to it. The sulcus terminalis divides the root of the tongue from the body of the tongue.

There are four types of lingual papillae – the filiform papillae, the fungiform papillae, the foliate papillae and the vallate papillae. All of these papillae bear taste buds except for the filiform papillae which we are going to discuss first.

So we're going to have a closer look at the filiform papillae by looking at this microscopic image of the tongue. The filiform papillae are these cone-shaped projections here but they can also take a cylindrical shape. They cover most of the presulcal area of the dorsum of the tongue and they're the most numerous of the lingual papillae. The main function of the filiform papillae is to increase the friction between food and the tongue and facilitate movement of particles by the tongue. As stated previously, these papillae don’t contain taste buds, therefore, they don’t participate in taste perception.

So, now, let's look at the fungiform papillae. The fungiform papillae are more sparse than the filiform papillae and are larger and rounded in shape. In fact, their name relates to their mushroom-like shape that you can see here. They are mostly found on the tip and the sides of the tongue and contain taste buds on their upper surface.

The third type of papillae we will look at today are the foliate papillae. The foliate papillae are vertical folds that are located bilaterally on the sides of the tongue near the sulcus terminalis. They can be described as leaf-like ridges of mucosa and they contain numerous taste buds. The foliate papillae are not very abundant in the human tongue.

So, now, we'll look at our fourth and final type of papillae – the vallate papillae. These papillae can also be referred to as the circumvallate papillae. The vallate papillae form a V-shaped row anterior to the sulcus terminalis. There are usually between eight and twelve of this type of papillae and, on this image, there are ten of them. If we have a closer look at these papillae, we can see that they're cylindrical structures and they're surrounded by this mucosal elevation or so-called wall. If we zoom in even further, we can see that the vallate papillae is separated from its wall by a circular sulcus here. This circular sulcus is known as the sulcus of papilla.

So, now, let's move on to look at the taste buds. As I said before, the taste buds are located on all of the lingual papillae except for the filiform papilla. They are also located on most of the dorsal and lateral surfaces of the tongue and occasionally on the soft palate and epiglottis. Most of the taste buds are located around the area of the vallate papillae just anterior to the sulcus terminalis. Taste buds contain taste receptors or gustatory receptors which interact with the chemicals in food to produce an action potential. Each taste receptor has the potential to one or more of the main categories of taste sensation. The categories of taste are considered to be sweet, salty, sour, bitter, and umami which is a Japanese translation for pleasant savory taste.

Taste is one of the five main human senses and along with smell, it helps us determine the flavor of food. Taste is brought to the brainstem by three different cranial nerves – the facial nerve specifically the chorda tympani for the anterior two-thirds of the tongue and the soft palate, the glossopharyngeal nerve for the posterior third of the tongue, and the vagus nerve for the epiglottis.

The next structure we will look at are the gustatory glands. The gustatory glands are also commonly known as Von Ebner's glands. These glands are salivary glands that are found around the vallate papillae and secrete a serous fluid. This fluid begins lipid hydrolysis and facilitates the perception of taste. Their location around the vallate papillae is important as it provides a continuous fluid over the high concentration of taste buds, which dissolves the food particles so they can interact with the taste receptors. This fluid also keeps the cleft created by the sulcus of papilla flushed to allow for the next taste. So, in this image, we can see the Von Ebner's glands located inferiorly to the vallate papilla.

There are some other glands we can see in this image here and these are known as the posterior lingual glands or the glandula radicis linguae. The posterior lingual glands are located in the root of the tongue which is the area of the tongue posterior to the sulcus terminalis. These glands secrete mainly mucous fluid. So I mentioned serous fluid when relating to the Von Ebner's glands and mucus fluid relating to the posterior lingual glands. I feel like here is worth distinguishing between the two. So, serous fluid is a thin watery secretion that contains protein such as the enzyme amylase and ions. Mucus is a much more thicker secretion. It contains glycoproteins, proteins and lipids.

So another structure that we can see in this image is the lingual tonsil. The lingual tonsil is a small mound of lymphatic tissue located at the back of the tongue. There is one lingual tonsil on each side of the tongue and they assist the immune system in preventing infection. Within the lingual tonsil, there are lymphoid nodules which we can see here highlighted in green. They contain B and T lymphocytes. These lymphocytes get activated when bacteria and viruses come in contact with the tonsils. The B lymphocytes produce antibodies against the pathogens whereas the T lymphocytes kill them by engulfing them.

The lingual tonsil is covered by stratified squamous epithelium that invaginates inward to form a tonsillar crypt. The posterior lingual glands are these glands that we mentioned earlier secrete mucus fluid into the crypt which keeps it clean and less prone to infection.

To conclude this tutorial, we'll go over some clinical notes related to some of the structures that we've looked at today. In some conditions, lingual papillae can be lost and this is called depapillation. This leaves a smooth red and sometimes tender tongue. Some diseases that cause depapillation include geographic tongue, median rhomboid glossitis, and nutritional deficiencies. The term glossitis is often used to refer to depapillation.

Transient lingual papillitis is an inflammatory condition that affects the fungiform papillae. It presents as a single painful white bump usually near the tip of the tongue and is usually self-resolving within a few days but can recur months or years later. The reduced ability to taste things is called hypogeusia whereas the complete lack of taste is known as ageusia. Dysgeusia is the distortion of the sense of taste. Hypogeusia and dysgeusia are commonly caused by zinc deficiency and certain drugs such as chemotherapy agents. These conditions must be differentiated from changes to sense of smell as these can also alter taste sensation. Ageusia can be caused by damage to the nerves that carry taste sensation to the brainstem especially the chorda tympani and the glossopharyngeal nerve.

Like other types of tonsils, the lingual tonsils can also get inflamed and this is known as lingual tonsillitis. Lingual tonsillitis can cause pain, redness, fever and dysphagia which means difficulty swallowing. It is usually caused by bacteria so antibiotics are often prescribed, although viruses can also cause it. Hypertrophy of the lingual tonsils can cause airway obstruction and sleep apnea. Treatment usually involves lingual tonsillectomy or removal of the tonsils.

Lingual tonsillectomy may also be indicated if the lingual tonsils become cancerous. The two main types of cancer that affect the lingual tonsils are squamous cell carcinoma and lymphomas. Risk factors include human papilloma virus, smoking, and alcohol.

And that brings us to the end of this tutorial. I hope you enjoyed it and thank you for listening.

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